Dick Johnson Racing will take an all-new driver line-up into the 2021 season.
Kiwi driver Scott McLaughlin has crossed another achievement off his bucket list.
"I love the sport and right now I'm pretty happy where I am at."
The championship leader drove superbly to finish third, after starting 12th at St Petersburg.
The Brit took the chequered flag first for the 92nd time in Portugal.
Meanwhile, Supercars champion Scott McLaughlin debuts on the US open-wheel circuit.
Scott Dixon struggled in qualifying, but so did his championship rival Josef Newgarden.
The Kiwi will not return to defend his Australian championship in 2021.
Scott McLaughlin will make his IndyCar debut in the season finale in Florida.